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Old 01-27-2013, 02:30 PM   #31 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post

In my opinion you want enough capacity for a single 0-70 acceleration event, as well as the capacity to recover the same energy in a single panic stop. This is your worst case scenario.


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Mech
How is extra energy dissipated if say you are traveling 85MPH or going down steep hill at 70MPH?


See you answered it while I was posting the question.


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Old 01-27-2013, 08:16 PM   #32 (permalink)
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Originally Posted by Old Mechanic View Post
I would think you would want to insulate the accumulator to conserve the heat energy for better overall efficiency.
Not just the accumulator ... every part of the system ... Hydraulic motor , Pump, transfer pipes, etc ... every joule of energy lost ( heat , sound , whatever ) is lost energy and lowered efficiency of the system.

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Originally Posted by Old Mechanic View Post
Ian made a good point about the efficiency of electric regeneration. My counterpoint is a worst case scenario where you are forced to make a panic stop. In 20 revolutions of the wheels you have to recover your several hundreds of horsepower-seconds of energy in a vehicle weighing over 1 ton. That basically means every revolution of each wheel needs to be able to recover about 10 horsepower seconds of energy in a total time of a few seconds. In this scenario I am not aware of any electric powered vehicle with this capability. Maybe the KERS system in the new Formula 1 designs, but at what cost?
Kinetic Energy = 1/2 m V^2
In Joules , kilograms , m/sec
1 ton = 2,000 pounds = ~909 kg
60 mph = ~96 kmph = ~27 m/s
~331,330 Joules = ~92 wh of energy.
If you can't store ~92 wh of energy than your system can only try to recover as many kwh of energy as it can store.

For example the KERS systems are limited to 400kJ of energy ( ~111 wh )... in 5kg of flywheel weight ( ~22wh/kg )

I you want to take 1 hour to stop needs ~92 watts of braking power.
In 1 minute = ~5,520 w = ~5.5 kw of braking power
It's really hard to keep enough traction to accelerate or decelerate faster than gravity 9.8 m/s^2.
Or about ~2.8 seconds
To brake 1 ton from 60 mph to 0 mph in ~3 seconds would require ~110 kw of braking power over those ~3 seconds ( ~132 feet ) ... if you can brake slower it takes less power.

The Kinetic energy is linear with Mass ... so 2 Tons would be double the braking power ~220 kw to stop in the same ~3 Seconds from 60 MPH.

Braking might get wind resistance , rolling resistance, gravity as some 'free' braking power ... depending on context.

Getting a ~110 kw rated EV is not especially hard ... if that is what one wants ... Tesla is more than this ... or 12kg EMRAX motors can do peaks of 80kw for ~1min ... two would more than cover the braking power in all of ~25 kg ... I don't know of any hydraulic motors or pumps that can match or beat the power density of EMRAX Electric Motors ... thus .. unless you know of a hydraulic motor I don't ... the motor part would weigh more than what is available today for an equally powered electric motor.

While not common ... there are EVs with motors and batteries that can do better than this.

Formula 1 KERS are also limited to 60kw... 24kg... and 13L of space ... 2.5 kw/kg & 4.6 kw/L ... fairly good but not the best... It's the 12 kw/kg power density of the flywheel that is the hard part for beating KERS ... Maybe with some high end capacitors... while the energy density ~22wh/kg of the flywheel is not great ... that 12kw/kg power density of the flywheel is a real monster.

If we are comparing power density of the Hydraulic accumulator to that of the power density of flywheels , or capacitors ... I think the hydraulic will have a hard time ... against chemical batteries ... that Will be much easier ... Not many Chemical Batteries have better than about about ~2 kw/kg power densities ... but that much kw/kg power density is still no small feat for hydraulic storage either... and if you leave the power density discussion to talk about energy density ... that is VERY hard for the hydraulic to compete against modern chemical battery tech.

But ... there are still other considerations ... Mean Time Before Failure ... $ ... etc... I don't think it is accidental or foolishness that battery based HEVs are currently more dominate in the market ... if that changes because something else got better for whatever reason ... fine / great ... be it hydraulic , flywheel , or whatever.

Last edited by IamIan; 01-27-2013 at 08:29 PM.. Reason: added 60-0 feet braking disatance
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Old 01-27-2013, 10:45 PM   #33 (permalink)
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Thanks Ian, I know I can count on you for a precise explanantion although it may be a little over my head technically speaking. Lets see if I got the message.

There are systems that could work with electricity and batteries that could compete with a hydraulic system, even exceed a hydraulic system that is state of the art to the best of your knowledge, of which I do not know how extensive your knowledge is relative to hydraulics, but I think it would be safe to assume it is substantial.

Now, my question is do you think it is practical to develop and produce the combination of electrical components you referred to and incorporate them into a vehicle that is practical and reliable, and if so at what cost? Not demanding precision in any way, but in your last paragraph you referred to reliability and cost as two factors that must be considered, which is the most important point, as any vehicle must be affordable to be successful.

In previous posts I have alluded to the fact (in my opinion) that a HH could be produced with sufficient capacity for normal use at a cost (after production reached a significant level) that would be no greater than any currently available low priced vehicle. Since we both share the same objective which is the highest percentage of vehicles available that are affordable and reliable, while we differ in possible the pathway to that vehicle, we both share a belief that such a vehicle should be produced as quickly as practical in any configuration that is reliable and cost effective.

I just believe that pathway is hydraulic and my design is based on the understanding of the sum of the objectives, but possibly biased towards the understanding that if the average driver can not afford it, it will never be commercially successful. Practical automobiles existed before the advent of the Model T Ford, but the Model T, while it was surpassed by almost all of the competition, was reliable, cheap, and repairable by a novice with simple tools. That is why it succeeded and Ford's dedication to efficiency in production maintained that advantage fro 1908 to the last Model T produced in 1927.

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Old 01-28-2013, 02:36 PM   #34 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post
In my opinion you want enough capacity for a single 0-70 acceleration event, as well as the capacity to recover the same energy in a single panic stop.
You know, I think you just made my argument for me :-)

Honestly, storing energy for just one acceleration just isn't going to cut it in a normal passenger car. Even the first generation hybrids could do a dozen accelerations, and nowadays you'd want 10-40 miles or so of non-petroleum range. Normal car drive cycles are also accelerate to speed, and drive for extended time with variable amounts of assist/regen climbing & descending hills, etc. Hydraulic hybrids are a bad match for this, just as they are a great match for the stop&go cycle of delivery trucks.

Also, your panic stop scenario is unrealistic. It is a rare event (or should be for a competent driver). so it'd be acceptable to waste the braking energy. But I do want to be able to climb a mountain - maybe not Pike's Peak, but say 4500 vertical feet - using reasonable assist all the way, and recapture much of that energy in the descent. The Insight doesn't quite manage that, but with 2-3 times as much battery storage, it would. A reasonable HH wouldn't even come close.

PS: For me, a panic stop might happen once a year or less, but significant climb/descent cycles - say 2500-4500 ft - happen several times a week.

Last edited by jamesqf; 01-28-2013 at 02:44 PM..
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Old 01-28-2013, 02:50 PM   #35 (permalink)
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Quote:
Originally Posted by IamIan View Post
It's the 12 kw/kg power density of the flywheel that is the hard part for beating KERS ... Maybe with some high end capacitors... while the energy density ~22wh/kg of the flywheel is not great ... that 12kw/kg power density of the flywheel is a real monster.
It would seem fairly simple (technically) to build a system with a flywheel as buffer between battery and motor. You'd want a capacity of 2X braking energy from highway speed, and aim to keep it at 1X...
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Old 01-28-2013, 09:20 PM   #36 (permalink)
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Quote:
Originally Posted by jamesqf View Post
It would seem fairly simple (technically) to build a system with a flywheel as buffer between battery and motor. You'd want a capacity of 2X braking energy from highway speed, and aim to keep it at 1X...
Yup.

It would also be fairly simple to build a capacitor bank as a buffer.

And it would also be fairly simple to build a battery pack that can itself handle the short term peak power demands without a buffer ... the more total energy storage one has , the less useful high power density becomes ... this is the direction most OEMs seem to be currently favoring... as the larger energy capacity has it's own additional benefits as well.

Which way works best or what design and in what application ... varies ... devil in the details.

Quote:
Originally Posted by Old Mechanic View Post
Thanks Ian, I know I can count on you for a precise explanantion although it may be a little over my head technically speaking. Lets see if I got the message.
Sorry if I poorly explained anything ... by all means ask and I will try and elaborate / clarify.

Quote:
Originally Posted by Old Mechanic View Post
There are systems that could work with electricity and batteries that could compete with a hydraulic system, even exceed a hydraulic system that is state of the art to the best of your knowledge, of which I do not know how extensive your knowledge is relative to hydraulics, but I think it would be safe to assume it is substantial.
yup...

Either platform could potentially be better than the other ... depending on the specifics of a specific design and build ... and what application that specific build was used in ... use the right tool for the job ... doesn't mean tool A is worse or inferior than tool B in general ... but for specific applications it might be ... using an chain saw to try and cut your bread is as bad as trying to use a bread knife to cut down a tree.

As for my knowledge ... I have no doubt other people know more than me about a great many things ... and I'm happy to learn ... I find the best method for both sides is for both sides to explain the reasons for their position ... then either side can potentially learn from the other about one thing or another... if I explain the reasons I think X , and someone sees an error in one or more of those reasons ... I get the chance to learn something ... maybe it is enough for me to change my mind about X ... or maybe on it's own it isn't enough ... but either way I've learned.

Energy efficiency in general has been an interest of mine my whole life ... So I am always happy to explore , research , experiment , etc ... about different methods and ways to squeeze out 1% more.

Quote:
Originally Posted by Old Mechanic View Post
Now, my question is do you think it is practical to develop and produce the combination of electrical components you referred to and incorporate them into a vehicle that is practical and reliable, and if so at what cost? Not demanding precision in any way, but in your last paragraph you referred to reliability and cost as two factors that must be considered, which is the most important point, as any vehicle must be affordable to be successful.
Yes.
But I don't think it is one sided either ... I think both platforms could be designed in a practical , reliable, and cost effective vehicle ... but they are not equal technologies in all things ... that isn't necessarily a bad thing ... one wants to use the right tool for the right job.

Quote:
Originally Posted by Old Mechanic View Post
I just believe that pathway is hydraulic and my design is based on the understanding of the sum of the objectives, but possibly biased towards the understanding that if the average driver can not afford it, it will never be commercially successful.
Back when HEVs first started the electric and battery option had enough of a technological and financial edge to get it's foot in the door first for the consumer vehicle application.

For any other platform to unseat it now would require a rather significant technological leap.

Even if we were to assume for the moment that hydraulic tech was 100% identically capable as the Electric + Battery option ... the investments have already been made for factories , supply chains , workers trained , products tested , built , sold , etc ... even if it were exactly the same it would not be a smart business choice to invest again in something that isn't significantly better than what one is already setup for.

Once it gets it's foot in the door first ... it feeds itself ... it gets more research funding for improvements ... it costs less due to economies of scale , and mass production already established ... etc ... etc.

It is only if a specific platform starts to run into serious scientific barriers and limitations that other smaller scale technologies have a chance ... this is what we saw with the ICE ... it started to run into more and more difficult issues to squeeze another 1% out of it... thus giving the chance for other smaller scale technologies.

- - - - - - -

The future can change ... of course... as science and technology changes , etc... or even without science of tech change ... market demand can change.

My personal point of view has a preference for the electric/battery option as the technology I am aware of stands today ... but I will happily admit that is completely dependent on the design and application ... it is not universal.

For me at least ... in terms of a vehicle to get from point A to point B ... when I think of the highest net efficiency platform to be able to do that application ... currently that is electrics and batteries from solar power ... all other options are currently significantly less net efficient ... and the electric / battery path for HEVs ... is a logical stepping stone for the technology to scale up with , get market acceptance etc ... then the PHEVs ... repeat ... than the BEVs ... repeat ... all the while more and more solar energy deployed... so for me ... my own personal energy efficiency bias ... due to current technology that I am aware of ... leads me away from hydraulics for vehicle point A to point B applications ... not all applications.

Of course a specific HH could be more net efficient than a straight ICE vehicle ... or even a specific HEV ... and if it is more efficient for a given application ... ... progress is progress.... and if you want to make that improvement of 1% of 10% , whatever it is ... for your own application ... ... great ... best of luck... please post all about it
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Old 01-28-2013, 09:39 PM   #37 (permalink)
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Quote:
Originally Posted by jamesqf View Post
You know, I think you just made my argument for me :-)

Honestly, storing energy for just one acceleration just isn't going to cut it in a normal passenger car. Even the first generation hybrids could do a dozen accelerations, and nowadays you'd want 10-40 miles or so of non-petroleum range. Normal car drive cycles are also accelerate to speed, and drive for extended time with variable amounts of assist/regen climbing & descending hills, etc. Hydraulic hybrids are a bad match for this, just as they are a great match for the stop&go cycle of delivery trucks.

Also, your panic stop scenario is unrealistic. It is a rare event (or should be for a competent driver). so it'd be acceptable to waste the braking energy. But I do want to be able to climb a mountain - maybe not Pike's Peak, but say 4500 vertical feet - using reasonable assist all the way, and recapture much of that energy in the descent. The Insight doesn't quite manage that, but with 2-3 times as much battery storage, it would. A reasonable HH wouldn't even come close.

PS: For me, a panic stop might happen once a year or less, but significant climb/descent cycles - say 2500-4500 ft - happen several times a week.
There's no need to store 2500-4500ft worth of energy, because you expend a lot of energy going down the hill, that's my opinion. I also don't believe in significant non-gasoline range, for cost/packaging reasons. If the gasoline drivetrain is reasonably efficient there's no need to go save those last few drops of fuel, it takes too long to pay for itself and increases the mass of the vehicle.
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Old 01-28-2013, 09:44 PM   #38 (permalink)
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I appreciate the time you spent in your response Ian and the rational consideration you give to the subject. If you have not already seen this my Patent #7677208 (US only) was issued close to 3 years ago this March. The design started out with a decent understanding of the advantages of in wheel drives which when driven hydraulicly mean lower RPM and higher efficiency. The stroke is adjustable from the central 0 position (neutral or freewheel) to one in either direction, giving forward, neutral and reverse (regenerate) positions in individual wheels without any need for any other power modulation, or clutching function. The drives can be directly connected to the accumulator.

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Mech

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Old 01-29-2013, 08:47 PM   #39 (permalink)
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I appreciate the time you spent in your response Ian and the rational consideration you give to the subject. If you have not already seen this my Patent #7677208 (US only) was issued close to 3 years ago this March. The design started out with a decent understanding of the advantages of in wheel drives which when driven hydraulicly mean lower RPM and higher efficiency. The stroke is adjustable from the central 0 position (neutral or freewheel) to one in either direction, giving forward, neutral and reverse (regenerate) positions in individual wheels without any need for any other power modulation, or clutching function. The drives can be directly connected to the accumulator.

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Mech
You're welcome ... like I said ... Progress is progress.

Nice
I wish you the best of luck in further implementation of it.

Have you in the 3 years been able to construct a working prototype of your hydraulic motor / pump design? ... If so have you yet been able to send it out for validating via 3rd party testing of the devise itself?

- - - - - - -

My own personal concern about any in-wheel motor ... ICE, Hydraulic, electric , whatever ... is that the wheel is just about the most abusive location on the car ... shock , heat, cold, impacts, submerged in water, etc ... etc... I'll agree there are advantages ... but those pros don't come without some cons too ... the abuse is a big one for long term durability.

Locating the hydraulic motor in the wheel like that also would make it very difficult to insulate it from heat loss due to compression of the working fluid ... if you throw away the heat energy from the compression , efficiency goes down with the lost joules of heat.

- - - - - - - -

A hydraulic Hybrid might find better traction along lines similar to what HEVs did ... combine it with existing vehicle components to reduce the net vehicle impact of implementation ... for HEV it was starter and alternator merged into one HEV motor to do both... and with the added low end Electric motor torque a smaller ICE could be used , also reducing the impact of implementation.

In theory the HH could get a few electric motors can't ... the brake pump is hydraulic for example ... and one might be able to even combine it with the heat pump functions of an air conditioning system.... etc.

- - - - - - - - -

The other thing to consider for a HH ... what is the incremental improvement path? ... HEV mild to full ... HEV Full to short PHEV ... short PHEV to long PHEV ... Long PHEV to BEV.... what is the incremental path for the HH? ... if it is a dead end at the HH ... it won't be as attractive for manufactures to invest heavily in it.
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Old 01-30-2013, 01:34 PM   #40 (permalink)
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There's no need to store 2500-4500ft worth of energy, because you expend a lot of energy going down the hill, that's my opinion.
Suggest you come out here and try driving down some of our hills, without using brakes or engine braking :-) Of course you don't need to store 100% of the energy needed to raise the weight of the vehicle that distance (though it would be nice). What you need is the capacity to store all the EXCESS energy that would otherwise be wasted in braking.

Quote:
don't believe in significant non-gasoline range, for cost/packaging reasons.
Your beliefs are not at issue. If you want a vehicle that doesn't have such capabilities, there are many on the market to choose from. I do want one, and am speculating on how best to design it.

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